With the development of display technology, the demand for image quality of display is increasing, and the demand for flat panel display apparatuses with high image quality and high resolution becomes more and more common and more and more attracts the attention of display panel manufacturers.
A thin film transistor (simply referred to as TFT) is a main driving device in a flat display panel. A low temperature poly-silicon (simply referred to as LTPS) has a relatively high mobility and stability, and its mobility may be up to tens or hundreds of times that of amorphous silicon. Therefore, techniques of forming thin film transistors with low temperature poly-silicon materials have been rapidly developed.
Low-temperature poly-silicon thin films (i.e., active layers) in low temperature poly-silicon thin film transistors (LTPS TFT) are typically formed by performing a process of excimer laser annealing (ELA) on amorphous silicon thin films. In the process of laser annealing, non-uniform crystal grain sizes of poly-silicon and large roughness on the surface of poly-silicon thin films may be caused, leading to bad uniformities of threshold voltages and mobilities of low temperature poly-silicon thin film transistors. In particular, when the size of a transistor reduces, the problem of non-uniform threshold voltages will become severer. Furthermore, a typical method is sequentially preparing a silicon nitride layer and a silicon oxide layer as buffering layers on a glass substrate, then depositing an amorphous silicon thin film, and then irradiating the amorphous silicon thin film with excimer laser having a wavelength of 308 nm. In the process of the conversion of amorphous silicon to poly-silicon, the crystal grain size is directly determined by the crystallization period, and thus a relatively thick buffering layer is required to achieve the object of temperature retention. At present, it has been proposed that a glass substrate is heated to elongate the crystallization period. However, the heat resistance of the glass substrate and a relatively thick heat insulating layer between a heating table and amorphous silicon (glass substrate and buffering layer) limit the temperature of the heating and the performance
There is still the need for methods and apparatuses for obtaining better low temperature poly-silicon thin films.